The invention is related to an apparatus for controlling the air-fuel quantity ratio in internal combustion engines. In a known apparatus of this kind, the diaphragm of the differential-pressure valve controls an outlet opening to a relief line in which there is a throttle at which a control pressure builds up for the actuation of a servo motor. As a result, the ratio of exhaust gas to fresh air is variable and the position of the fuel metering throttle device and of the fuel metering cross section is variable in accordance with the thus-varied fresh-air component. A preliminary supply pump is also provided for the fuel supply of the fuel injection pump. The supply pressure of this preliminary pump is held constant because this pressure serves at the same time to generate the constant restoring force which is exerted on the air flow rate meter.
It is a precondition for the desired mode of operation of this known apparatus that the entire fuel quantity traversing the metering cross section is carried via the fuel supply line to the injection pump and from there is also delivered to the combustion chambers of the internal combustion engine, so that the controlled air-fuel ratio can be maintained. The fuel injection pump can, accordingly, not be flushed or cooled with fuel which is flowing back to the fuel supply container, which is otherwise conventional. A means of cooling is possible, as also provided in the known apparatus, only by means of a supplementary cooler, by which fuel is diverted out of the injection pump chamber housing the pump piston drive means (which in many cases also serves as the intake and fuel supply chamber for supplying and relieving the pump working chambers) to the intake side of a supply pump additionally provided in the injection pump. This supply pump, in the known constructions of injection pumps, acts to generate a supply pressure in the injection pump chamber which varies in accordance with the engine speed.